Preheat oven to 225 degrees F. Line baking sheet with parchment paper. Set aside.
In the bowl of a food processor, add basil leaves and kosher salt. Pulse until basil leaves are ground. Spread mixture out evenly on prepared baking sheet. Bake for 20-30 minutes until mixture is dry.
Break up any clumps that may have formed with your fingers. If necessary, pulse mixture in food processor to a fine powder. Store in an air tight container.
Preheat oven to 500 degrees F. If using a pizza stone, place in oven at this time.
If using store bought pizza dough, let come to room temperature.
Spread olive oil in 12-inch cast iron skillet. Place room temperature pizza dough in oiled skillet and gently push and pull dough to fit skillet.
Spread 2-3 tablespoons of pesto on pizza dough, leaving about 1/2'' border around the pizza. Sprinkle half of the mozzarella over pesto. Arrange tomato slices onto and follow with remaining mozzarella. Season with basil salt and black pepper.
Transfer skillet to stove over high heat. Warm up the cast-iron skillet. Cook the pizza for about 3 minutes until the bottom of the crust has set and the oil is bubbling along the outer rim of the pizza.
Transfer hot skillet into preheated oven. Bake for 7-10 minutes until cheese has melted and is bubbling.
Remove from oven and let sit for 2-4 minutes before unmolding pizza. Place pizza on cutting board and use a sharp knife or pizza wheel to cut into slices. Garnish with additional basil salt, if desired.
*basil salt adapted from Food Network Magazine Aug 2012
Keep basil salt in an airtight container at room temperature. Use within one month for best flavor.